电子结构方法中带结构特征值问题的统一视角

在(相对论)电子结构方法中，四元数矩阵特征值问题和计算激发能的线性响应(Bethe-Salpeter)特征值问题是两个经常出现的结构特征值问题. 尽管前一个问题已被十分仔细地研究，后一个问题在一般形式下，即不假设电子Hessian正定性的复矩阵情况，并没有得到完全的理解. 鉴于它们非常相似的数学结构，本文从一个统一的角度研究了这两个问题，揭示了它们特征向量的“李群”结构，为将来设计对角化算法和数值优化方法提供了一个统一的框架. 利用和处理四元数矩阵特征值问题相同的归约算法，本文给出了表征线性响应问题特征值(实数、纯虚、或复数)的充分必要条件. 这一结果可以看作是实矩阵情况下已知条件的自然推广.

Structured Eigenvalue Problems in Electronic Structure Methods from a Unified Perspective

In (relativistic) electronic structure methods, the quaternion matrix eigenvalue problem and the linear response (Bethe-Salpeter) eigenvalue problem for excitation energies are two frequently encountered structured eigenvalue problems. While the former problem was thoroughly studied, the later problem in its most general form, namely, the complex case without assuming the positive definiteness of the electronic Hessian, was not fully understood. In view of their very similar mathematical structures, we examined these two problems from a unified point of view. We showed that the identification of Lie group structures for their eigenvectors provides a framework to design diagonalization algorithms as well as numerical optimizations techniques on the corresponding manifolds. By using the same reduction algorithm for the quaternion matrix eigenvalue problem, we provided a necessary and sufficient condition to characterize the different scenarios, where the eigenvalues of the original linear response eigenvalue problem are real, purely imaginary, or complex. The result can be viewed as a natural generalization of the well-known condition for the real matrix case.